Factor: x4−16x^4 - 16x4−16.
(x+2)2(x−2)2(x + 2)^2(x - 2)^2(x+2)2(x−2)2
(x2+4)(x2−4)(x^2 + 4)(x^2 - 4)(x2+4)(x2−4)
(x2+4)(x+2)(x−2)(x^2 + 4)(x + 2)(x - 2)(x2+4)(x+2)(x−2)
(x2−4)2(x^2 - 4)^2(x2−4)2